The effect of injecting a calcium-calmodulin independent form of myosin light chain kinase (IMLCK) was studied using 3T3 fibroblasts. No obvious conclusions could be drawn as to whether the kinase had a consistent effect on cell shape or movement. These studies are continuing at Carnegie Mellon University in an effort to obtain consistent results with a greater number of cells. Treatment of 32P-labeled chicken embryonic fibroblasts did not appear to result in an increase in the phosphorylation of MLCK, but did result in a decrease in the phosphorylation of the 20 kDa light chain of myosin. When similar experiments were conducted with primary cultures of rat aortic smooth muscle cells, there was both an increase in MLCK phosphorylation and a decrease in the phosphorylation of the 20 kDa myosin light chain. However, no evidence was obtained for a causal relation between these observations, nor was the extent of phosphorylation quantitated.